You Know the Flux application in SMT ,Effect and Classification

A. Flux Effect

1. Using a reduction reaction in Chemistry  to remove the surface oxides of the base metal and the brazing and soldering alloy to create conditions for the wetting and spreading of the liquid soldering alloy on the base material.

2. The flux can protect the surface of the base metal and the solder alloy before the soldering is completed to prevent secondary oxidation.

3. Before the welding is completed, the flux is often covered with a thin layer of liquid on the surface of the base metal or even the solder alloy. Therefore, the flux must have a certain heat transfer capacity to ensure that the heat of welding can be effectively transmitted to the welded portion.

4. Flux can act as an interface to improve the wetting and spreading ability of the liquid soldering alloy to the base metal.

5. The flux should have sufficient ability to remove the oxide film on the surface of the base metal and the solder alloy within the soldering temperature range, which is the most basic requirement for the flux.

6. Flux should have a wide range of active temperatures and good thermal stability.

7. The density of the flux and its active product should be less than the density of the solder alloy.

8. Flux and its residue should not have strong corrosive effect on the base metal and solder joints, nor should it be toxic or precipitate harmful gases during use.

9. The flux residue after soldering should meet the no-clean standard or can be easily cleaned.

B. Flux classification

1. Rosin (RO) Resin (RE) Organic (OR) Inorganic (IN) IPC: J-STD-004

2. No-clean fluxSIR: under the test conditions specified in IPC-TM-6502.6.3.3 (85 ° C / 85% RH, 165 h, -100 v) > 100 megohms

3. Technical indicators and testing of fluxa.

a).Appearance color

Colorless, pale yellow, brown, yellow, light greenb.

b).The proportion of flux

0.80g/ml 1.0g/mlc.

c). Solid content

2.0%-7.0%d.

d).Acid value of the flux

The number of milligrams of KOH (17-35 mg KOH/g) required to neutralize 1 g of flux